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Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
Kategorie: Wissenschaft und neue Technologien
Sprache: Englisch

Beschreibung

Written by world-renowned experts on the topic with many years of research and consultancy experience, this invaluable book provides the practitioners' perspective, outlining the dangers and benefits of static electricity in industry.
The first chapter reviews the fundamentals of understanding fires and explosions in general and electricity-induced ignition in particular, while the following chapter is dedicated to the origins of static electricity in industrial settings, such as in flowing gases and the transport of disperse systems. The major part of the text deals with measuring static electricity, elimination of unwanted charges and hazard prevention under different conditions. It concludes with an overview of practical applications in chemical and mechanical engineering. Throughout the book, real-life case studies illustrate the fundamental aspects so as to further an understanding of how to control and apply static electricity and thus reduce material damages as well as increase occupational safety.
Plus additional movie sequences on the dedicated website showing static electricity in action.

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Leseprobe

Cover

Title Page

About the Authors

Opening Remark

Preliminary Remarks

Preface

Chapter 1: Basics of Fire and Explosion: Risk Assessment

1.1 Basic Considerations on Fire and Explosion ( T1)

1.2 Explosive Atmosphere

1.3 Hybrid Mixtures ( P7)

1.4 Allocation of Explosion-Endangered Areas and Permissible Equipment ( P6)

1.5 Permissible Equipment (Equipment Protection Level)

1.6 Ignition Sources

1.7 Minimum Ignition Energy (MIE)

1.8 Imaginary Experiment to Assess the Hazardous Potential of Flammable Liquids

PowerPoint Presentations

References

Chapter 2: Principles of Static Electricity

2.1 Basics

2.2 Electrostatic Charging of Solids ( T2)

2.3 Triboelectric Series

2.4 Surface Resistivity

2.5 Electrostatic Charging of Liquids ( T2, T8)

2.6 Charging by Gases

2.7 Electric Field

2.8 Electric Induction ( T3)

2.9 Capacitance and Capacitor

PowerPoint Presentations

References

Chapter 3: Metrology

3.1 Basics ( T7)

3.2 Appropriate Metrology for Electrostatic Safety Measures

3.3 Comparison: Electrostatics/Electrical Engineering

3.4 Selecting the Suitable Measurement Methods

3.5 Assignment and Summary

3.6 Conductivity of Liquids

3.7 Bulk Materials

3.8 Concerning the Use of Insulating Material in Endangered Areas

3.9 Measurement of Electrostatic Charges

3.10 Other Measurement Applications

3.11 Capacitance

3.12 Themes around Air Humidity

PowerPoint Presentations

Picture Credits

References

Chapter 4: Gas Discharges

4.1 Mechanisms of Gas Discharges ( T5)

4.2 Electrostatic Gas Discharges

4.3 Types of Gas Discharges

4.4 Consequences of Gas Discharges

4.5 Listing of Traces Caused by Gas Discharges ( P11; T8)

4.6 How Can Dangerous Gas Discharges Be Avoided?

PowerPoint Presentations

Video Credits

References

Chapter 5: Preventing Electrostatic Disturbances

5.1 Electrostatics: When Sparks Fly

5.2 Dielectric Strength

5.3 Discharging Charged Surfaces

5.4 Potential Hazards Posed by Discharge Electrodes

Picture Credits

Video Credits

References

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Guide

Cover

Table of Contents

Preface

Begin Reading

List of Illustrations

Chapter 1: Basics of Fire and Explosion: Risk Assessment

Figure 1.1 Danger triangle.

Figure 1.2 Vapor pressure/temperature curve of ethanol.

Figure 1.4 Minimum ignition energy subject to the stoichiometric ratio.

Figure 1.3 System of flammable liquids (up to 2009).

Figure 1.5 Correlation between flash point and

− 1 – condition.

Chapter 2: Principles of Static Electricity

Figure 2.1 Opposite charges attract each other and like charges repel each other.

Figure 2.2 Charge dissipation.

Figure 2.3 Charging before contact.

Figure 2.4 Charging by contact.

Figure 2.5 Charging by contact and subsequent separation.

Figure 2.6 Triboelectric series.

Figure 2.7 Median of charges at a separating speed of 1 m/s.

Figure 2.8 Surface resistivity

(Ω) of various plastics at 50% RH and 23 °C.

Figure 2.9 Correlation of surface resistivity

and air humidity.

Figure 2.10 Nonconductive liquid in metal vessel.

Figure 2.11 Charged ions are dragged along with the liquid flow.

Figure 2.12 Electrical field lines in a parallel plate capacitor.

Figure 2.13 Electric field lines (solid) between parallel conductive plates in combination with equipotential lines (dashed).

Figure 2.14 Electric field lines in a cylinder–plate configuration combined with equipotential lines.

Figure 2.15 Practical utilization of field lines (solid) and equipotential lines (dashed).

Figure 2.16 Sequence of electric induction.

Figure 2.17 Charged particle establishes image charge at a conductive object.

Figure 2.18 Isolated screw charged by electric induction.

Chapter 3: Metrology

Figure 3.1 Measurement of leakage resistance at flooring

Figure 3.2 Performance and result of a walking

Figure 3.3 Influencing factors for electrical resistance.

Figure 3.4 Guard ring circuit for fault prevention when measuring the volume resistance.

Figure 3.5 Common electrode configuration for surface resistance.

Figure 3.6 Guard ring circuit for fault prevention when measuring the surface resistance.

Figure 3.7 Attracting forces (

) between charges of opposite polarity and repelling forces (

) between charges of like polarity.

Figure 3.8 Schematic diagrams of static voltmeters.

Figure 3.9 Electrometer amplifier.

Figure 3.10 Charge measurement by means of a Faraday pail.

Figure 3.11 Charge measurement on free-falling droplets, test rig, and resulting diagram.

Figure 3.12 Principle basic configuration of induction electric field meters (with permission of F7).

Figure 3.13 Electro field meter by Kleinwächter GmbH (with permission of F7).

Figure 3.14 Charge on unrolling foil.

Figure 3.15 Undistorted electrical field around a charged foil.

Figure 3.16 Field distortion when approaching an earthed measuring device (with permission of F2).

Figure 3.17 Field homogenizing on one side (with permission of F2).

Figure 3.18 Homogenizing of the electric field on both sides of the foil (with permission of F2).

Figure 3.19 Measuring error caused by earthed parts (wooden desk) nearby (with permission of F2).

Figure 3.20 Measuring error caused by earthed parts (metal roller) nearby (with permission of F2).

Figure 3.21 Principle of Kasuga Denki KSD System (with permission of F3).

Figure 3.22 Block diagram of surface voltmeter (with permission of F3).

Figure 3.23 Measurement of field strength by means of potential adaption.

Figure 3.24 Principle of piezo technology for potential-free measurement (with permission of F4).

Figure 3.25 Trek contact voltmeter (with permission of F5).

Figure 3.26 Measuring area E-field meter Ø 20 mm (with permission of F1).

Figure 3.27 Measuring area piezo sensor (with permission of F5).

Figure 3.28 Induction electric field meter modified as a voltmeter (with permission of F2).

Figure 3.29 Voltmeter up to ±40 kV (precision ±2.5%) (with permission of F7).

Figure 3.30 Modified induction electric field meter as a Coulomb meter (with permission of F2).

Figure 3.31 Modified ball electrode.

Figure 3.32 Electric induction field meter as a picoampere meter (with permission of F2).

Figure 3.33 Measurement of surface charge on a moving web (with permission of F2).

Figure 3.34 Test procedure with triboelectric charge [9]. (a: fixed clamping unit; b: field intensity meter; c: cylinder rods; d: test sample; e: guide rail; f: tensioning device; g: slide start position).

Figure 3.35 Test procedures with electrostatic influence (with permission of F2).

Figure 3.36 Front view of ICM-2 by the Saxony Textile Research Institute e.V. (STFI) (with permission of F6).

Figure 3.37 Charged plate monitor (with permission of F7).

Figure 3.38 Charged plate monitor with earthed plate (with permission of F7).

Figure 3.39 Configuration of the paper test procedure as defined by Knopf [6] (with permission of F2).

Figure 3.40 Measurement configuration for charging bulk material (with permission of F2).

Figure 3.41 Electrostatic charging on filling the tank (with permission of F2).

Figure 3.42 Measurement of electrostatic charges in a spray tower (with permission of F2).

Figure 3.43 Block diagram of a capacitance meter.

Figure 3.44 The voltage curve of the measured object (see Section M10.3).

Figure 3.45 Charge decay measurement as defined by Künzig (with permission of F2).

Figure 3.46 Charge decay measuring device QUMAT

-528 (with permission of F16).

Figure 3.47 Air temperature versus dew point at parameter RH.

Figure 3.48 Dew point hygrometry (with permission by F8).

Figure 3.49 Psychrometer.

Figure 3.50 Principle of LiCl moisture detector.

Chapter 4: Gas Discharges

Figure 4.1 Gas discharge between ball electrodes.

Figure 4.2 Partial plasma effect with gas discharge.

Figure 4.3 Photo of a gas discharge with partial plasma.

Figure 4.4 Collapsing of electric and magnetic fields bring about a radio signal.

Figure 4.5 Grounded emitter.

Figure 4.6 Loop dipole.

Figure 4.7 Spark discharging of a capacitor.

Figure 4.8 Principle of corona discharging.

Figure 4.9 Principle of brush discharging.

Figure 4.10 Cone discharge in a silo (1: super charged bulk material, 2: conductive silo, earthed, 3: cone discharges).

Figure 4.11 Bipolar charged foil.

Figure 4.12 Charging by striking particles (shielded).

Figure 4.13 Charging by striking particles (unshielded).

Figure 4.14 Propagating brush discharge (with permission of F9).

Figure 4.15 Spark at a liquid surface (V4.2).

Figure 4.16 Enamel coatings with conductive layer. Comment of this example: Pfaudler BE6300 reactor with 20 m

glass-lined surface. (1) Electrostatic energy discharges from the process into the earthed reactor body. (2) Electrostatic charge migrates through the cover coat by capacitance without damaging. (3) Electrostatic charge is then spread over the large surface of the conductive glass layer. (4) The 1 mm cover coat is not penetrated, thus preventing the lining from being damaged. (5) External earthing of the conductive layer removes any electrical potential difference . Charging/discharging time of capacitor with (with permission of F10).

Figure 4.17 Occurrences of different gas discharges.

Chapter 5: Preventing Electrostatic Disturbances

Figure 5.1 Charge-emitting discharge electrode (with permission of F2

Figure 5.2 Clean and corroded points (with permission of F2).

Figure 5.3 Passive ionizers (earthing chain/earthing tongues) (with permission of F2).

Figure 5.4 Passive ionizer with capacitive coupling (with permission of F2).

Figure 5.5 Illustration of field line concentration for the ionization of the air (with permission of F2).

Figure 5.6 The charge profile is made visible – Lichtenberg Figure (lycopodium on plexiglass).

Figure 5.7 Triboelectric effect from contact and separation (with permission of F2).

Figure 5.8 Propagating brush discharge during the rerolling process (with permission of F23).

Figure 5.9 Discharge electrode over the delta film web reel (with permission of F2).

Figure 5.10 Optimal discharging setup during unwinding/rewinding (with permission of F2).

Figure 5.11 Optimal placement of discharge bars (with permission of F2).

Figure 5.12 Single-sided discharging – unfavorable (with permission of F2).

Figure 5.13 Double-sided discharging – optimal (with permission of F2).

Figure 5.14 Bipolar layers of equal field strength (with permission of F2).

Figure 5.15 Disrupting the bipolar field strengths of equal height permits discharging (with permission of F2).

Figure 5.16 Example 1 of multilayer material.

Figure 5.17 Example 2 of multilayer material.

Figure 5.18 Ionization blower head used to increase separation rate (Eltex R55 shown in image) (with permission of F2).

Figure 5.19 Discharging on sheeting machinery (with permission of F2).

Figure 5.20 Discharge electrode with a large effective range (with permission of F11).

Figure 5.21 The “CombiCleaner” operating principle (with permission of F12).

Figure 5.22 Ionization blower head on a handling system (with permission of F2).

Figure 5.23 Rotary nozzle with discharge electrode for hazardous areas (ATEX approved) [4] (with permission of F2).

Figure 5.24 Discharging electrodes on a set of weighing scales (with permission of F13).

Figure 5.25 Charge on granules (with permission of F2).

Figure 5.26 Paper disposal (with permission of F2).

Figure 5.27 Bulk transport (with permission of F2).

Figure 5.28 Discharging blower above a feeder bowl (with permission of F13).

Figure 5.29 Discharging above a feeder bowl (with permission of F2).

Figure 5.30 Discharge electrode with resistive and capacitive current limiter [6] (with permission of F2).

Figure 5.31 Dirty discharge electrodes that no longer function and that may have lost their ATEX approval (with permission of F2).

Figure 5.32 Bearing damage on a rolling bearing from a spark discharge.

Chapter 6: Description of Demonstration Experiments

Figure 6.1 Attentive dog.

Figure 6.2 Voltmeter.

Figure 6.3 Field meter.

Figure 6.4 Van de Graaff generator.

Figure 6.5 Explosion tube.

Figure 6.6 Rolling pipes – 1.

Figure 6.7 Rolling pipes – 2.

Figure 6.8 Rolling pipes – 3.

Figure 6.9 Hovering pipes – 1.

Figure 6.10 Hovering pipes – 2.

Figure 6.11 Electroscope.

Figure 6.12 Field lines.

Figure 6.13 Charging by separation – 1.

Figure 6.14 Charging by separation – 2.

Figure 6.15 Charging by separation – 3.

Figure 6.16 Charging of single particles in metal pipe.

Figure 6.17 Charging of single particles in PTFE pipe.

Figure 6.18 Charging of many particles.

Figure 6.19 Basic experiment on induction.

Figure 6.20 Chimes.

Figure 6.21 Plastic vessel with shielding.

Figure 6.22 Glass apparatus.

Figure 6.23 Checking on dissipating properties.

Figure 6.24 Charged person causes sparks.

Figure 6.25 Ignition voltage.

Figure 6.26 Spark discharges.

Figure 6.27 Corona discharges.

Figure 6.28 Brush discharges.

Figure 6.29 Brush discharges in a fluorescent lamp.

Figure 6.30 Evidence of ion wind.

Figure 6.31 Propagating brush discharges – 1.

Figure 6.32 Propagating brush discharges – 2.

Figure 6.33 Ignition of dust.

Figure 6.34 Short circuit of a double-layer charge.

Figure 6.35 Demonstration of a propagating brush discharge at a double-layer charge.

Figure 6.36 Demonstration of flash point.

Figure 6.37 Concentration gradient.

Figure 6.38 Progressive flame front.

Figure 6.39 Oxygen demand – 1.

Figure 6.40 Oxygen demand – 2.

Figure 6.41 Gasification process with wood.

Chapter 7: Case Studies

Figure 7.1 Emptying PE-bag.

Figure 7.2 Plastic inner liner.

Figure 7.3 Sieving machine.

Figure 7.4 Spray-bed-dryer.

Figure 7.5 Discharges on creeping oil film. (V4.2)

Figure 7.6 Throttle valve.

Figure 7.7 Filling

-hexane.

Figure 7.8 Hose filter.

Figure 7.9 Fire in water hose.

Figure 7.10 Lost shovel in a silo.

Figure 7.11 Fire in PE-drum.

Figure 7.12 Terminal box (opened).

Figure 7.13 Incoming sunbeam.

Chapter 8: Targeted Use of Charges

Figure 8.1 Charge emitting charging bars

Figure 8.2 The distribution of forces in opposite- and similar-poled charges [1].

Figure 8.3 Load on a plate capacitor

Figure 8.4 Fixing of decorative films/decorative papers to plates

Figure 8.5 Illustration showing the fixing of paper on a metal band

Figure 8.6 Ply blocking of chipboard

Figure 8.7 Fixing of coverings on an MDF plate (medium-density fiberboard)

Figure 8.8 Blocking systems [3].

Figure 8.9 Charging with plate electrodes (example: Stack blocker AVN VB 70, Affeldt Maschinenbau GmbH, www.affeldt.com).

Figure 8.10 Schema and implementation for the adhesion of an insert on a variable base

Figure 8.11 Ribbon charging by the charging bars

Figure 8.12 Melt layer adhesion using a wire electrode on a chill roll

Figure 8.13 Melt layer adhesion by edge zone fixing (point charging) on the chill roll (anti-neck-in)

Figure 8.14 Anti-neck-in with charging bar (Eltex ATR23), film 12 µm at 600 m/min.

Figure 8.15 Avoiding telescoping when winding using electrostatic charging

Figure 8.16 Core dummy charge

Figure 8.17 Direct charge using electrodes

Figure 8.18 Indirect charge

Figure 8.19 Oil application on metal sheets

Figure 8.20 Aerosols are misted from the laminar air boundary layer (V8.4, with permission of F2).

Figure 8.21 Aerosols are attracted from the charged web

Figure 8.22 Heat and material transport on a web

Figure 8.23 Breakup of a laminar airflow as described by F. Knopf

Figure 8.24 Gravure printing and coating machines with electrostatic assistance

Figure 8.25 Schematic diagram of a coating machine [5]. Key: 1, drying system; 2, impression cylinder; 3, ionizing bar; 4, powerful brush discharge; 5, low brush discharge (without No. 3: powerful brush discharge); 6, coating unit (zone 0 with highly flammable liquids); 7, winding systems (unwinder/rewinder); 8, dust; 9, floor; dissipative in Zone 1.

Figure 8.26 Coating machine with print cylinders with different diameters

Figure 8.27 Variable coverings to reduce the escape of ink particles

Figure 8.28 Highly charged ink particles deposited in the electrical field (Lichtenberg deposits)

Figure 8.29 Schematic diagram of ink deposits in the electrical field

Figure 8.30 Ink deposits glow

Figure 8.31 Ink particle deposits

Figure 8.32 Five roller coating system (example).

Figure 8.33 Misting tacker as described by F. Knopf

Figure 8.34 Operating principle of the Optical-Web-Tension-Profile-Scanner.

Figure 8.35 Results of a web tension profile measurement

Figure 8.36 Material separation.

Figure 8.37 Example of the operating principle of an electrostatic precipitator

Figure 8.38 Low-energy plasma on a double pin array

Figure 8.39 Device for precipitating impurities from a stream of gas

Figure 8.40 Principle of operation of Grabit’s electroadhesion technology (with permission of F20).

Figure 8.41 Corona system with ceramic electrodes that have been extracted

Figure 8.42 Grafting of organic groups on the surface of polymer film

Figure 8.43 Configuration of active discharging electrodes after a corona system.

List of Tables

Chapter 1: Basics of Fire and Explosion: Risk Assessment

Table 1.1 Threshold of oxygen concentration for some gases and dusts with two kinds of inert gases (volume percent oxygen).

Table 1.2 Criteria for flammable liquids.

Table 1.3 Flammable liquids, classification, and labeling.

Table 1.4 Relationship between zone, category, and EPL.

Table 1.5 Classification of combustible gases into temperature classes.

Table 1.6 Classification of combustible gases into explosion groups.

Table 1.7 Increase of surface by fragmentation.

Table 1.8 Exemplary liquids.

Table 1.9 Minimum ignition energy (MIE) correlating with minimum ignition charge (MIQ) [4].

Chapter 2: Principles of Static Electricity

Table 2.1 Liquids of low conductivity (relaxation time in seconds).

Table 2.2 Liquids of medium conductivity (relaxation time in milliseconds).

Table 2.3 Liquids of high conductivity (relaxation time in microseconds).

Chapter 3: Metrology

Table 3.1 Comparison between electrical engineering and electrostatics.

Table 3.2 Criteria for the selection of the measuring voltage.

Table 3.3 Assignment of resistance values.

Table 3.4 Conductivity values of selected liquids.

Table 3.5 Liquids of low conductivity.

Table 3.6 Liquids of high conductivity.

Table 3.7 Groups of bulk materials.

Table 3.8 Charge build up on powders.

Table 3.9 Permittivity

Table 3.10 Temperature and saturation.

Table 3.11 Humidity calibration solutions.

Chapter 4: Gas Discharges

Table 4.1 Boundary limits for the characterization of solid materials and examples for the classification of objects.

Table 4.2 Maximum allowed isolated capacitance in equipment for zones with explosive atmosphere.

Table 4.3 Restriction on size of insulating solid materials in hazardous areas.

Table 4.4 Maximum accepTable transferred charge.

Table 4.5 Influences for gas discharge.

Table 4.6 Ignition potential of electrostatic gas discharges.

Chapter 5: Preventing Electrostatic Disturbances

Table 5.1 Restriction on size of insulating solid materials in hazardous areas [5].

Chapter 7: Case Studies

Table 7.1 Ignition sources.

Table 7.2 Alternative restrictions on insulating solid materials and isolated conductive or dissipative parts in hazardous areas for equipment within the scope of IEC/TS 60079-0:2011 [5]

Chapter 8: Targeted Use of Charges

Table 8.1 Impact of misting tacker.

Static Electricity

Understanding, Controlling, Applying

Günter Lüttgens, Sylvia Lüttgens, and Wolfgang Schubert

Authors

Günter Lüttgens

Research and Consulting

Am Berg 27

51519 Odenthal

Germany

Sylvia Lüttgens

Research and Consulting

Am Berg 27

51519 Odenthal

Germany

Wolfgang Schubert

SCHUBERT GMD

Publicly Appointed and Sworn Expert for

Printing Technologies

Print-Machines Printability and Runnability Packaging Print

Independent appraiser for Electrostatics

Weidenweg 15

04425 Taucha

Germany

Cover material was kindly provided by the authors

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.d-nb.de.

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978-3-527-34128-3

ePDF ISBN: 978-3-527-80332-3

ePub ISBN: 978-3-527-80334-7

Mobi ISBN: 978-3-527-80335-4

oBook ISBN: 978-3-527-80333-0

Cover Design Formgeber, Mannheim, Germany

About the Authors

Günter Lüttgens was born in Berlin, 1933, and holds a master’s degree in electrical engineering. Since graduation he mainly worked in the chemical industry in the field of electrostatics. He was primarily responsible for laboratory research, as well as plant safety, in the area of fire and explosion prevention. In 1998, he was nominated by IEC as an expert for electrostatic test methods. For more than 25 years he gave lectures on static electrification and safety measures together with his wife Sylvia. He published several articles and specialist books. In 2013, he received the International Fellow Award by the European Working Party (EFCE) as a researcher and teacher in the field of “Static Electricity in Industry.”

Sylvia Lüttgens was born in Geroda, 1946, was graduated a teacher, and tried to direct the interest of her students to Music and English. Then she learned about static electrification and that it could be the cause for many a fire or an explosion. So she has been working together with her husband Günter, carrying out experimental lectures (up to 2015) in seminars about electrostatics, giving practical proof of the theory. Besides, she is publishing articles and writing specialist books on this topic.

They actually compiled the first encyclopedia on static electricity 15 years ago, and the third edition was published in 2013.

Wolfgang Schubert was born in 1952. He studied print technology in Leipzig and is a trained printer. He became self-employed in 1997 having previously worked in various managerial roles in the print industry and in sales and marketing for manufacturers of roll- and sheet-fed printing presses. Since then he has also been working in the specialized field of electrostatics, in sales and marketing and also in further education. He has coauthored the specialist publication Static Electricity.

In May 2016, he was publicly appointed and inaugurated by the Leipzig Chamber of Commerce and Industry (IHK) as an expert in the fields of printing processes, printing presses, printability, runnability, and packaging printing. He also works as an expert in the field of electrostatics.

Opening Remark

Minds of Felix – our faithful companion

May I introduce myself; I am Felix the electrostatics specialist dog (see Figure 6.1 in Section 6). When my humans are carrying out seminars, I silently lie under the tables with the experimental devices until Sylvia prepares the one in which a plastic tumbler is flung into the air by an explosion in an explosion tube (see Section 6.11.1). Then, I run for the tumbler and noisily chew it apart, which makes the audience laugh.

When my humans Sylvia and Günter are working at the computer, I often lie on the sofa watching them. When I have had enough of it, I fetch my teddy and place it in front of them. Then, they throw it somewhere, and I have to find it. This happens several times but then I take my teddy and jump back onto the sofa again. My humans think I am doing this because I am bored, but this is not true! I feel sorry for them that they have to sit in front of the computer with lots of paper, clattering the keys, writing this specialist book. So I have to offer them some variety. I know what this is all about, and I am definitely responsible for my pack.

Preliminary Remarks

In this specialist book, Videos and PowerPoint Presentations are referred to.

The Videos are indicated with “V” and listed at the end of the relevant chapters and may be downloaded from www.wiley-vch.de/xxx.

For better comprehension, at different places animated PowerPoint Presentations are referred to with the symbol (). The letter T stands for theory and P for practice.

These presentations may be requested from the authors:

G. & S. Lüttgens: [email protected]

W. Schubert: [email protected]

Preface

It gives me a great pleasure to preface this excellent reference book for engineers and technicians. Sylvia Lüttgens, Günter Lüttgens and Wolfgang Schubert are well known for their very didactic manuals, excellent presentations and so well prepared demonstrations such way that rather complicate phenomena seem simple.

This reference book on Electrostatic Hazards for engineers and technicians is, in my knowledge, the first one with very clear explanations, describing step by step the phenomenon with very didactic concepts and perfect pedagogic demonstrations.

Electrostatic Hazard is a very worrying problem in a lot of industrial processes, using liquids, granular material, powders, or foils etc. It concerns a wide range of industries: Chemical, Petroleum, Pharmaceutical industry, as well as the agricultural sector and electric power plants.

Indeed, in recent decades many industrial processes increasingly use electrically insulating materials. These materials such as polymers have emerged with the petroleum products industry and have played a growing importance in industry because of their lower costs like metals and their easier processing, manufacturing and use. This has partly led to the fact that these materials and products brought about electrostatic hazards and nuisances and have become an important concern. When speaking about electrostatics, everyone has in mind the spark which we sometimes feel by touching the door of a car after being parked; or small pieces of paper attracted to a plastic wall that has been rubbed before. In fact, electrostatic charging in general is the study of electrical phenomena when the charges are not moving (“static”). However, at present, the so-called electrostatic phenomena are those involving electrification processes whereby often charge accumulation due to the use of insulating materials and product takes place.

The electrostatic hazards are sources of dangers of electric discharges due to electrostatic phenomena. Under certain conditions, these discharges lead to ignitions causing fire or explosions. Electrostatic nuisances cause degradation of an industrial process due to electrostatic effects. Precondition for this is that the generated charge will be accumulated.

Charge generation is, in principle, related to contact of material and separation thereafter as, e.g., friction, flow, transfer of solids, or liquids. The accumulation is the result of the storage or collection of such products or liquids in unearthed containers.

Unfortunately electrostatic hazards may result in fatal accidents, injuries, often serious, especially burns, property damage, often important or significant in that case, for example, of fire extension to nearby facilities.

This reference book has a very logical and scientific methodology, making these interrelations very clear and useful for engineers and technicians. Indeed, it starts with the situations with the Risk Assessment, explaining precisely when and where such risks come into being. Then the basics of Static Electricity are presented, developing all the concepts and equations which are needed to understand the different phenomena. In another chapter the metrology, needed to understand the different situations, is presented. The processes of the different gas discharges are then exposed as well as different methods to prevent electrostatic disturbances. One important subject of the book is the presentation of very didactic descriptions of demonstration experiments and of case studies.

It would fall short of that goal to hold static electricity accountable only for dangers and nuisances, however, electrostatic mechanisms are used in many applications where one would not expect them as there are: photocopying techniques, car body lacquering etc. Widely used is static electricity in improvements of many different scopes of application like wetting, drying, printing etc. Therefore one chapter is dedicated especially to that task to motivate the curious reader to improve other technologies with the help of static electricity.

Finally a very useful mathematic toolbox is given at the end of the book, making an easy understanding of all equations needed to comprehend the different processes.

Each chapter provides a complete bibliography of what was stated.

And in the good end, I have spent a pleasant time to read this very educational and didactic reference book that I strongly recommend to any engineer and technician who wants to learn on Electrostatics.

Prof. em. Gerard Touchard University Poitiers, Groupe Electrofluidodynamique [Institute PPRIME] Poitiers, France October 2016

Chapter 1Basics of Fire and Explosion: Risk Assessment

If static electricity was really static, as one may assume by its name, then it could be ignored. Only when it becomes more dynamic does it appear to be interesting and extend in our awareness from harmless electric shocks, sometimes felt when leaving a car, to the possibly fatal lightning strokes of a thunderstorm (for the latter, there is detailed information given in www.lightningsafety.noaa.gov).

However, our intention in this book is to demonstrate that the obviously weak electrostatic discharges are more or less capable of igniting combustible materials, thus causing hostile fire and casualties. It is probably because of its unpredictability that static electricity is often incorrectly blamed as a cause of fire and explosion when no other plausible explanation is at hand. So it seems logical to start with basics on fire and explosion.

1.1 Basic Considerations on Fire and Explosion ( T1)

In which way do fire and explosion differ from one another?

Common to both is the manifestation of a flame, which always indicates a fast combustion of fuel/air mixtures in the gaseous phase. The chemical reaction, depending on the combustion heat of the fuel, leads to an increase in temperature.

Fire is characterized mainly by a stationary burning flame in an open atmosphere, for example, a lighted candle. Therefore the reaction heat spreads into the surroundings without increase in pressure.

However, when an ignition occurs in a combustible atmosphere within an enclosed space, for example, a drum, a flame front runs through the entire space, starting from the ignition source. Under atmospheric conditions, the flame front extends at a speed of 10 m/s. Therefore the heating effect of the flame causes a pressure increase of about 10 bars, which diminishes during subsequent cooling. It is decisive that this short time pressure increase may cause a devastating damage called explosion.

The exothermic reaction of fuel in air occurs between the tiniest particles, that is, the molecules of fuel and oxygen. This is the case when prevailing fuel gas forms the required gaseous phase. With flammable liquids, this molecular fuel/oxygen mixture can easily be achieved by vaporization of the liquid. However, for solid fuels (dusts, but not metal dusts), it is necessary to break their chemical bonds so that hydrocarbon molecules are set free to react with oxygen. Therefore a considerable part of the ignition energy is used for melting, vaporizing, or cracking the dust particles to gaseous hydrocarbons. This is the reason why much more energy is always needed to ignite flammable dusts than is necessary to ignite flammable gases and vapors.

On the contrary, at metal dusts an oxidization at the particle surface takes place, which is exothermic as well.

Basically a fire or an explosion will occur when the following components coincide with time and volume, which is known as the “danger triangle” (see Figure 1.1):

Fuel

Oxygen

Ignition source (heat)

Figure 1.1 Danger triangle.

This danger triangle is used worldwide mainly to show that three components are required to cause a fire, and if one of them is missing, combustion will not occur. Looking more into details, it is necessary to meet the additional conditions for each component.

1.1.1 Fuel

In this context fuel stands for the material that causes an explosive atmosphere. Although it is necessary to distinguish between gaseous, liquid, and solid fuels, a common feature between them is that combustion is sustained only within a certain explosion range, which is determined by the lower and upper explosion limits. For flammable liquids, the lower explosion limit is characterized by the so-called flash point (see Figure 1.2). Between the lower and the upper explosion limits, an explosive atmosphere always prevails.

Figure 1.2 Vapor pressure/temperature curve of ethanol.

1.1.2 Heat

In this context heat stands for the thermal energy needed to start an ignition, also called an ignition source (see Figure 1.4).

1.1.3 Oxygen

For all fuels, a minimum oxygen concentration (MOC) in air is necessary below which combustion cannot occur.

1.1.4 Inerting Process

It is worth mentioning the “MOC,” which is defined as the threshold of oxygen concentration below which combustion is impossible. It is expressed in units of volume percent of oxygen and is independent of the concentration of fuel (see Table 1.1). But it is to be noted that the MOC varies with pressure and temperature and is also dependent on the type of inert gas.

Table 1.1 Threshold of oxygen concentration for some gases and dusts with two kinds of inert gases (volume percent oxygen).

Gas or dust

Nitrogen/air

Carbon dioxide/air

Ethane

Hydrogen

Isobutane

Methane

-Butane

Propane

PE-HD

—

PE-LD

—

Paper

—

PMMA

—

PVC

—

1.1.5 Heat versus Oxygen

It has to be pointed out that there is an interrelation between the oxygen concentration and the energy of the ignition source: the higher the oxygen concentration, the lower the need for ignition energy and vice versa.

1.2 Explosive Atmosphere

1.2.1 Explosion Limits with Flammable Liquids

In preventing fire and explosion in general, explosion limits are important. This can be explained by a simple experiment in which some lamp kerosene is poured into a small coquille: when a lighted match is dipped into the liquid, it becomes extinguished. Obviously lamp kerosene is fuel!

However, when this experiment is repeated after the lamp kerosene is heated up to 45 °C, the lighted match causes an ignition, and the liquid continues to burn at its surface.

The explanation for the behavior of the lamp kerosene in the aforementioned experiment has to do with the vapor pressure of the liquid. Depending on the temperature of the liquid, a certain vapor pressure, and hence vapor concentration, is developed above the surface of the liquid. Figure 1.2 shows the vapor pressure temperature curve for ethanol and the relation between the vapor concentration at the surface of the liquid and its temperature. As ethanol is indicated by a flash point of 12°C the above mentioned experiment would lead to a flame already at room temperature.

By using the curve, temperatures can be assigned to the lower and upper explosion limits of a liquid. The temperature related to the lower explosion limit is called the flash point (°C) and is a simple and reliable way of defining the danger of flammable liquids in view of their ease of ignition. Liquids at a temperature lower than their flash point cannot be ignited. Therefore, the flash point ranks as the most important data when using flammable liquids and is listed in safety data sheets, for instance, indicating that they will not burn at room temperature.

In the example for ethanol, the explosion danger exists only within the explosion range, which is limited by the lower explosion temperature (12 °C) and the upper one (37 °C). After ignition, the flame spreads through the entire volume without any further fuel or air access. Also, it has to be taken into consideration that ignition is not possible above the upper explosion temperature. The fuel/air mixture is, so to speak, too rich, because of a lack of oxygen. This effect is used, for example, in gasoline tanks for cars. They will never explode but may burn down when there is a leakage (access to air).

Below the lower explosion limit, the average distance between fuel molecules to each other in air is too large; hence, by means of radiation from the ignition source, no sufficient energy can be transferred to continue the ignition (the decrease of energy by radiation follows the square of the distance). Above the upper explosion limit, the concentration of fuel molecules is so high that there is no enough oxygen between them for a reaction to take place.

In this context, it has to be stated that all vapors of flammable liquids show a higher density than air; thus they will always accumulate at the bottom of a vessel.

1.2.1.1 Classification of Flammable Liquids

Until 2009 the classification for flammable liquids depicted in Figure 1.3 was valid.

Figure 1.3 System of flammable liquids (up to 2009).

In 2009 flammable liquids were classified as hazardous substances and so have been covered in the United Nations Globally Harmonized System (GHS) of Classification and Labelling of Chemicals (UN 2013) [1].

The aim of the GHS is to have the same criteria worldwide for classifying chemicals according to environmental and physical hazards (see Table 1.2).

Table 1.2 Criteria for flammable liquids.

1.2.2 Explosion Limits with Combustible Dusts

In contrast to gases and vapors, mixtures of solid fuels (combustible dusts) and air are inhomogeneous because of the effect of gravity on particles; for example, with dusts in air, the particle distribution is not constant with reference to time and space. In terms of safety, the explosion limits for dust/air mixtures are not as critical as those for vapor/air and gaseous/air mixtures.

For most combustible organic dusts, the lower explosion limit ranges between 20 and 50 g/m3. However, there are a few very sensitive dusts with a lower explosion limit down to 10 g/m3. For instance, a few millimeters of combustible dust settled on the floor may present an explosion hazard in the entire room when swirled up by a draft of air. To determine an upper explosion limit is difficult as it ranges in concentrations of 1 kg/m3 and above.

1.2.3 Metal Dusts

Finely dispersed airborne metallic dust can also be explosive in so far as the metal itself tends to oxidize.

In contrast to the aforementioned organic dusts, transfer into the gaseous phase is not necessary to ignite metal dusts because they react exothermally directly at their surfaces with the oxygen in air.

1.3 Hybrid Mixtures ( P7)

An increased ignition danger always exists when powder products are combined with combustible gases or vapors because the ignition energy of the latter is lower on most occasions. Furthermore it has to be taken into consideration that hybrid mixtures are already combustible when the concentration of the dust as well as that of the gas is lower than their respective explosion limits. The needed energy to ignite hybrid mixtures is always lower than that of the pure dust cloud. Hybrid mixtures are to be expected, for example, when the powder is wet with flammable solvents.

1.4 Allocation of Explosion-Endangered Areas and Permissible Equipment ( P6)

In the ATEX 137 “Workplace Directive,” the minimum requirements for improving the safety of workers potentially at risk from explosive atmospheres are laid down.

The plant management must divide areas where hazardous explosive atmospheres may occur into “zones.” The classification given to a particular zone and its size and location depends on the likelihood of an explosive atmosphere occurring and its persistence if it does.

An explosive atmosphere can be divided into zones according to IEC 60079-10-1 and 60079-10-2 [2]:

Zone 0: Area in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapor, or mist is present continuously or for long periods or frequently

Zone 1: Area in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapor, or mist is likely to occur in normal operation occasionally

Zone 2: Area in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapor, or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only

Zone 20: Area in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously or for long periods or frequently for short periods

Note: Areas where piles of dust are present but where dust clouds are not present continuously, or for a long period, or frequently are not included in this zone.

Zone 21: Area in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur occasionally in normal operation

Zone 22: Area in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but if it does occur will persist for a short period only

1.5 Permissible Equipment (Equipment Protection Level)

An equipment category indicates the level of protection provided by the equipment to be used according to zones ( T6).

Here, areas in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapor, or mist prevails are indicated with the letter G (gas). Correspondingly, areas in which an explosive atmosphere in the form of a cloud of combustible dust in air exists are indicated with the letter D (dust).

1.5.1 Classification of Equipment Protection Level That Is Currently in the Introductory Stage

As already discussed, explosive atmospheres are divided into zones based on the probability that such an atmosphere will occur. But experience has shown that in some situations, a risk assessment would give the plant operator more flexibility. On this account and to facilitate a dependable risk assessment approach to make equipment selection easier, “equipment protection levels” (EPLs) have been introduced. EPLs identify and characterize all equipments according to the ignition risk they might produce.

According to IEC60079-0:2011 [3], equipment for use in explosive atmospheres is classified into the following EPLs (with distinguishing signs such as M for mining, G for gases, and D for dusts).

EPL Ma

: Equipment for installation in a mine susceptible to firedamp, having a “very high” level of protection, which has sufficient security that it is unlikely to become an ignition source in normal operation, during expected malfunctions, or during rare malfunctions, even when left energized in the presence of an outbreak of gas

EPL Mb

: Equipment for installation in a mine susceptible to firedamp, having a “high” level of protection, which has sufficient security that it is unlikely to become a source of ignition in normal operation or during expected malfunctions in the time span between there being an outbreak of gas and the equipment beingde-energized

EPL Ga

: Equipment for explosive gas atmospheres, having a “very high” level of protection, which is not a source of ignition in normal operation, during expected malfunctions, or during rare malfunctions

EPL Gb

: Equipment for explosive gas atmospheres, having a “high” level of protection, which is not a source of ignition in normal operation or during expected malfunctions

EPL Gc

: Equipment for explosive gas atmospheres, having an “enhanced” level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences

EPL Da

: Equipment for explosive dust atmospheres, having a “very high” level of protection, which is not a source of ignition in normal operation, during expected malfunctions, or during rare malfunctions

EPL Db

: Equipment for explosive dust atmospheres, having a “high” level of protection, which is not a source of ignition in normal operation or during expected malfunctions

EPL Dc

: Equipment for explosive dust atmospheres, having an “enhanced” level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences

It can be expected that in the future EPL will take the place of zones. Table 1.4 shows the relationship between zone, category, and EPL.

Table 1.4 Relationship between zone, category, and EPL.

Zone

1.6 Ignition Sources

Ignition sources are, according to scientific knowledge and experience, the means of releasing energy that is capable of igniting certain combustible materials when mixed with air. In the early 1960s, the evaluation of innumerable fire and explosion events had already shown that there were only 13 different ignition sources to be considered. Since then, various experts have experimented with ignition sources but have found it impossible either to reduce the number by combining ignition sources of the same nature or to find new ones. Today, 50 years later, the efforts of many experts throughout the world confirm that there are, indeed, only 13 ignition sources to deal with. They are listed in the following with short practical examples. However, it should be noted that it does not rank the ignition sources according to their frequency of occurrence.

1.6.1 Hot Surfaces

Hot surfaces arise as a result of energy losses from systems, equipment, and components during normal operation. In the event of a malfunction, the temperature may increase. Examples include coils, resistors, or lamps, hot equipment surfaces, brakes, or overheating bearings.

1.6.2 Flames and Hot Gases (Including Hot Particles)

Flames and hot gases including hot particles can occur inside combustion engines devices during normal operation and outside when a fault has taken place. Protective measures are required, for example, exhaust cooling devices.

Examples include autogenous welding and exhausts from internal combustion engines or particles, which are caused by switching sparks of electrical power lines.

1.6.3 Mechanically Generated Sparks ( MGS)

Mechanically generated sparks (MGS) come into being during grating, striking, and grinding actions when particles are cut off from solid materials. Due to the energy used for the separating process, particles will have a higher temperature. If these particles consist of oxidizable material (e.g., iron), they may reach temperatures up to 1000 °C on their flight path caused by the reaction with atmospheric oxygen, thus becoming sparks. MGS are capable of igniting flammable gases and dust atmospheres.

1.6.4 Electrical Apparatus

In general electrical apparatus are regarded as an ignition source. Exceptions are electrical devices containing only intrinsically safe circuits.

1.6.5 Cathodic Protection

Cathodic protection is an efficient and durable corrosion protection of metal equipment. Therefore it has to be taken into account that the used earthed voltage suppliers can result in stray electric currents, which then may bring up potential differences between different earthing points, possibly causing electric sparks.

1.6.6 Static Electricity

Static electricity is an ignition source that is often neglected, therefore making it the topic of this book.

1.6.7 Lightning

The impact of lightning can result in the ignition of an explosive atmosphere. However, there is also a possibility of ignition due to the high temperature reached by lightning conductors. Large currents flowing from lightning strikes, for example, via a lightning conductor, can produce an induction voltage into conductors in the vicinity of the point of impact, thus causing electrical sparks.

1.6.8 Electromagnetic Field

Electromagnetic waves have high frequency ranging from 104 Hz to 3 × 1011 Hz. Examples include transmitting and receiving equipment and mobile telephones.

1.6.9 Electromagnetic Radiation

Electromagnetic radiation is a form of energy that includes infrared radiation, visible light, and many more. Examples include photoflash, laser, and lamp for night vision devices.

1.6.10 Ionizing Radiation

Examples of ionizing radiation include X-rays for material testing and UV rays for radiation-induced polymerization.

1.6.11 Ultrasonics

Examples of ultrasonics include ultrasonic material testing and ultrasonic cleaning equipment.

1.6.12 Adiabatic Compression and Shock Waves

Examples of adiabatic compression and shock waves include starting a compressor in opposite direction and drift waves in long pipes.

1.6.13 Chemical Reactions

Examples of chemical reactions include exothermic processes.

Concerning theignitability of ignition sources, there are some that are capable of igniting all combustible materials (e.g., flames, lightning stroke). However, it is different in hot surfaces, mechanical sparks, and static electricity. These can only ignite certain combustible materials, depending on particular parameters, such as the ignition temperature and the minimum ignition energy (MIE) of the material (see Table 1.5).

Table 1.5

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